The present invention relates to fluorescent lamps and more particularly to fluorescent lamps including a reflector layer.
Various coatings of non-luminescent particulate materials have been found to be useful when applied as an undercoating for the phosphor layer in fluorescent lamps. In a fluorescent lamp, the phosphor coating is disposed on the inner surface of the lamp glass envelope in receptive proximity to the ultraviolet radiation being generated by the mercury discharge. The luminous efficiency of such lamps is improved by back reflection of the incident radiation being emitted from the phosphor layer.
Examples of non-luminescent particulate materials which have been used as reflector layers in fluorescent lamps such as, for example, aperture fluorescent reprographic lamps, include titanium dioxide, mixture of titanium dioxide and up to 15 weight percent aluminum oxide, aluminum, and silver. Titanium dioxide is typically used for the reflector layer in commercially available aperture fluorescent reprographic lamps. Preferred materials chosen to act as the reflector layer do not absorb either incident ultraviolet radiation or visible radiation being emitted by the phosphor.
In some instances a reflector layer is used to permit reduction in the phosphor coating weight. See, for example, U.S. Pat. No. 4,079,288 to Maloney et al., issued on 14 Mar. 1978. U.S. Pat. No. 4,074,288 discloses employing a reflector layer comprising vapor-formed spherical alumina particles having an individual particle size range from about 400 to 5000 Angstroms in diameter in fluorescent lamps to enable reduction in phosphor coating weight with minor lumen loss. The lamp data set forth in the patent, however, shows an appreciable drop in lumen output at 100 hours.
There still remains a significant need for further improvement in lumen output of a fluorescent lamp including a reflector layer during the lifetime of the lamp.